High tension cable barriers are used to guard against traffic accidents caused when a vehicle crosses a median on a highway system. These cable systems, made by several different manufacturers, typically use three-quarter-inch (19 mm) diameter, three-by-seven strand cable ropes, that may or may not be pre-stretched depending on the system, and posts to guide the cables through and maintain cable height. If a crash occurs, the posts are designed to break off and the cables redirect or stop vehicles to significantly reduce crash severity. The cable systems usually include three or four cable tiers and each of the cables has two ends that must be terminated and the cables tensioned, for example, to a tension of several thousand pounds (e.g., 5600 pounds). The termination of the cables must be sufficient to withstand the pretension force on the cable, as well as the forces and vibrations that the cable is subjected to when a vehicle hits it.
Designing these cable terminations has not been without challenges. The cables are a different shape and basic construction than is used in many other cable tensioning applications, such as post-tensioning concrete structures where a standard seven wire post-tension strand is used. Such post-tension strands have a relatively round profile. In high-tension median cable barrier systems, the cable is three twisted strands, each made of seven strands twisted together, and the three, seven strand cables are twisted together to make a cable rope that has a three-lobed profile.
The three-lobed rope is illustrated in FIGS. 1 and 2. It is specified as a 19-3×7 wire rope and conforms to the requirements of AASHTO M30 Type 1 Class A coding 19 mm wire rope. The rope, with connecting hardware attached, is specified to develop 110 kN strength of a single cable. It is particularly specified to be used as the rail element in cable guard rails on highways, particularly in the median, to prevent vehicles from crossing the median into the oncoming lane of traffic.
A cable wedge fastener is used to terminate the end of the wire rope so that it can be connected to either a turnbuckle for tensioning the wire rope or to another tension-related device to adjust or maintain the tension in the wire rope. Prior wedges for fastening such wire ropes typically had a seven-degree taper on the wedges and the wedges were configured in a manner such that pull-out of the cable ends from the termination was more likely than presently acceptable. The present invention provides an improvement to such prior wedge-style terminations.
Another type of cable termination is disclosed in U.S. Pat. No. 4,899,499, the disclosure of which is hereby incorporated by reference. The anchor disclosed has a body with a wedge shaped (conical) internal bore surface, a three section cable gripper with a wedge shaped (conical) external surface received in the bore, a cable gripped by the grippers and extending from one end of the body, a threaded cap at the end of the body opposite from the cable, a threaded stem extending from the cap outside of the body at the end opposite from the cable and the stem having a head that is captured against the interior facing surface of the cap. The stem is threaded into an insert that is embedded in a concrete structure or otherwise affixed to a relatively immovable structure. The termination disclosed in the references appears to be particularly adapted to grip post-tensioning strand of the type described above, being made of seven twisted wire bundles, with one of the bundles in the middle and the other six bundles twisted around the middle bundle.
Another problem with cable terminations of this type is corrosion inside the anchor. For example, corrosion can occur between the grippers in the body, between the cable and the grippers, and between the cap and the stem, which can ultimately reduce the tension in the cable and the grip of the termination on the cable.